Alison - As a frequent naturist, I'd be more worried about wearing something sutable for St Pat's night than the actual nudity. Why not make three large shamrock leaves to attach to the suitable places on a bikini (green if you have one that colour) ? If you don't mind being a bit more daring - how about using body-paint for the shamrocks. Alternatively wear a black leotard with a frothy white top and say you're a pint of Guiness !